The ENSO and QBO Impact on Ozone Variability and Stratosphere-Troposphere Exchange Relative to the Subtropical Jets

The El Nino-Southern Oscillation (ENSO) and the Quasi-Biennial Oscillation (QBO) are natural sources of ozone variability in the tropical and midlatitude upper troposphere and lower stratosphere. Regional tropospheric ozone variations have previously been attributed to ENSO- and QBO-induced changes in stratosphere-troposphere exchange around the subtropical jets (STJs). We use Goddard Earth Observing System Data Assimilation System analyses of Ozone Monitoring Instrument and Microwave Limb Sounder ozone data mapped to a STJ coordinate to examine the influence of ENSO and QBO on global and regional variability of upper troposphere and lower stratosphere ozone, and tropopause folding stratosphere-troposphere exchange. These coordinates eliminate the apparent variability due to the changing location of the STJ, which is itself influenced by ENSO. The ENSO influence on ozone variability near the STJ and in tropopause folds is much greater than the QBO influence, although both are small in a hemispheric mean. On regional scales, the ozone sensitivity to ENSO associated with tropopause folding is strongly positive in some regions and strongly negative in others, which largely cancel in the hemispheric mean. Poleward of the STJs, the sensitivities of stratospheric ozone to ENSO and QBO are large and similar in magnitude but are opposite in phase. Thus, the ozone responses to ENSO and QBO can largely cancel or reinforce, depending on their relative phases. These results can be used to evaluate and compare modeled QBO and ENSO influences on ozone variability that removes the first-order impact of differences in the location of the STJs.